Electrically operated lens shutters used in various types of photographic and laboratory equipment are well known in the art. Lens shutters especially adapted for use in scientific applications can open and close in a fraction of a second; frequencies of 2 to 400 cycles per second and higher are common.
Lens shutters generally are of two types. In one type, a so-called “guillotine” shutter has one or two thin, metal blades or leaves arranged to cover a lens opening. Pivot connections allow each blade to swing between a closed position where the blades cover the lens opening and an open position where the blades are drawn aside from the lens opening.
The present invention concerns a second type of shutter wherein a plurality of pivotally mounted blades, usually five, is arranged around the lens. Each blade is connected to a rotatable ring. In the operation of these rotary shutters, the rotation of the ring in one direction causes the blades to swing in unison to an open position. Counter rotation of the ring swings the blades to a closed position over the lens opening after exposure. Generally, a linear electric motor is used to activate the shutter. When activated, the linear motor pulls on a lever arm that rotates the ring to open the shutter. To close the shutter, the motor is deactivated and a spring causes the counter rotation of the ring to close the shutter. As noted above, shutters of this sort can cycle open and close several hundred times per second.
It is common in both types of shutters to provide a shock absorber or damper that absorbs the impact as the blades are pivoted between the open and closed positions. In this respect, reference is made to various US patents including U.S. Pat. Nos. 3,595,553; 3,664,251; and 6,652,165, the disclosures of which are incorporated herein by reference. As disclosed in these references, the shock absorber operates to stop the shutter blade very rapidly, yet softly and without damage. There also is little or no bounce as the shutter first is snapped open by the linear electric motor and then is snapped closed by the spring when the motor is deenergized.
In some applications, however, it is desirable to hold the shutter open for an extended period to prolong the exposure time. In these cases, it has been the practice to keep the motor activated for the duration of the exposure in order to hold the shutter open against the bias of the spring urging the shutter to a closed position.
Maintaining power to the coil of a linear electric motor for an extended period has its drawbacks due mainly to the resulting generation of heat. If not dissipated, the heat could adversely affect the alignment of the optics, cause image distortion and shorten the life of the motor and other heat sensitive components of the shutter system. A fan, heat sink or heat dissipating fins that normally can solve a heat-generating problem are not appropriate in many applications. For example, fans are of little use if the shutter is located in a vacuum environment. In military and space exploration applications, weight can be an issue so the use of any additional component such as a heat sink or heat radiating fins is not appropriate.
In some applications, space also is a limitation. Space limitations particularly in the region of the shutter opening dictate the parameters of size and placement of apparatus for holding the shutter open. For example, components placed near the shutter opening must have a relatively low profile so as not to interfere with the cone angle of the light passing through the open shutter.
Accordingly, it is an object of the present invention to provide an improved photographic shutter and, in particular, a high-speed rotary shutter having long exposure capabilities.
Another object of the present invention is to provide a rotary photographic shutter that allows long exposures without generation of excessive heat.
Yet another object is to provide a rotary shutter that does not automatically close once power to the motor operating the shutter is cut off.
A further object is to provide a rotary photographic shutter that is bi-stable in that it remains latched in either an open or a closed position until power is applied to a motor to specifically open or close the shutter.